LibGodot: Core - Build Godot Engine as a Library

* Add a new GodotInstance GDCLASS that provides startup and iteration commands to control a Godot instance.
* Adds a libgodot_create_godot_instance entry point that creates a new Godot instance and returns a GodotInstance object.
* Adds a libgodot_destroy_godot_instance entry point that destroys the Godot instance.

Sample Apps: https://github.com/migeran/libgodot_project

Developed by [Migeran](https://migeran.com)

Sponsors & Acknowledgements:

* Initial development sponsored by [Smirk Software](https://www.smirk.gg/)
* Rebasing to Godot 4.3 and further development sponsored by [Xibbon Inc.](https://xibbon.com)
* The GDExtension registration of the host process & build system changes were based
  on @Faolan-Rad's LibGodot PR: https://github.com/godotengine/godot/pull/72883
* Thanks to Ben Rog-Wilhelm (Zorbathut) for creating a smaller, minimal version for easier review.
* Thanks to Ernest Lee (iFire) for his support

Co-Authored-By: Gabor Koncz <gabor.koncz@migeran.com>
Co-Authored-By: Ben Rog-Wilhelm <zorba-github@pavlovian.net>

platform/linuxbsd/detect.py

@@ -67,7 +67,7 @@ def get_doc_path():
 def get_flags():
     return {
         "arch": detect_arch(),
-        "supported": ["mono"],
+        "supported": ["library", "mono"],
     }